Single Abstract Method Equivalent to a Trait? - scala

Question

Consider this trait:
trait Foo {
def m1(id : Int) : Try[String]
}
And an instance of this:
val g : Foo = new Foo {
override def m1(id: Int): Try[String] = Success("Good job")
}
Intellij offered a suggestion that this could converted to a Single Abstract Method:
val g : Foo = (id: Int) => Success("Good job")
Are these two equivalent and how?

Answer 1

Lets check what the scalac do for:
import scala.util.{Success, Try}
trait Foo {
def m1(id : Int) : Try[String]
}
object MainClass {
val g : Foo = new Foo {
override def m1(id: Int): Try[String] = Success("Good job")
}
}
run:
$ scalac -print src/main/scala/MainClass.scala
and output:
[[syntax trees at end of cleanup]] // MainClass.scala
package <empty> {
abstract trait Foo extends Object {
def m1(id: Int): scala.util.Try
};
object MainClass extends Object {
private[this] val g: Foo = _;
<stable> <accessor> def g(): Foo = MainClass.this.g;
def <init>(): MainClass.type = {
MainClass.super.<init>();
MainClass.this.g = {
new <$anon: Foo>()
};
()
}
};
final class anon$1 extends Object with Foo {
override def m1(id: Int): scala.util.Try = new scala.util.Success("Good job");
def <init>(): <$anon: Foo> = {
anon$1.super.<init>();
()
}
}
}
And do the same steps for:
import scala.util.{Success, Try}
trait Foo {
def m1(id : Int) : Try[String]
}
object MainClass {
def main(args: Array[String]): Unit = {
val g : Foo = (id: Int) => Success("Good job")
}
}
run:
$ scalac -print src/main/scala/MainClass.scala
output:
[[syntax trees at end of cleanup]] // MainClass.scala
package <empty> {
abstract trait Foo extends Object {
def m1(id: Int): scala.util.Try
};
object MainClass extends Object {
private[this] val g: Foo = _;
<stable> <accessor> def g(): Foo = MainClass.this.g;
final <artifact> private[this] def $anonfun$g$1(id: Int): scala.util.Try = new scala.util.Success("Good job");
def <init>(): MainClass.type = {
MainClass.super.<init>();
MainClass.this.g = {
((id: Int) => MainClass.this.$anonfun$g$1(id))
};
()
}
}
}
As you can see they are not the same for compiler.
In the first case, it is an anonymous object in second it is an anonymous function.